1. Technical Field
This invention relates generally to the reproduction of originals having both continuous-tone segments and other content segments, and more particularly to the discrimination of continuous-tone image segments.
2. Background Art
In reproducing originals using an electrophotographic reproduction apparatus, it is desirable to reproduce continuous-tone information segments of the original by halftone screening in order to extend the tone scale of the electrophotographic process. However, screened areas of the image outside the continuous-tone segment in an already halftoned segment may create objectionable density known as "moire." In addition, where line-type information such as alphanumerics, logos, etc. is to be reproduced, it is desirable that this image information not be modulated by the halftone screen during the imaging process.
In U.S. Pat. No. 4,740,818, issued to G. Tailibes et al. on Apr. 26, 1988, apparatus and methods are described for producing reproductions from originals having continuous-tone segments and segments of other content types, such as halftone and/or line-type information. Coordinate signals are created by the operator to identify the position of an image segment to be screened. In response to the signals, a light source, independent of the imaging light source, forms an electrostatic latent halftone pattern on a portion of an image frame area of the photoconductive member which is to form the reproduction of the halftone screened area without the light source reproducing a screen pattern in other areas of the image frame.
While operator-created coordinate signals for identifying the continuous-tone segments of the original are effective, this process is time consuming, and is difficult to do in conjunction with an automatic recirculating document feeder. The Tailibes et al. patent also discloses an autocorrelator capable of distinguishing high frequency halftone information from other types of information, and means for discriminating between line-type and low frequency screened halftone information of the one hand and continuous-tone information on the other. Details of the autocorrelator and the discriminator can be found in U.S. Pat. No. 4,194,221, which issued to J. Stoffel on Mar. 18, 1980. The present invention provides an improved way to locate segments of an original document which have continuous-tone information.